Man-made carbon-dioxide emissions are of little significance in the global concentration of carbon dioxide in the atmosphere and the effect of carbon dioxide concentration on global climate is of even less significance. In fact it is much more likely that CO2 concentrations in the atmosphere follow global temperature rather than the other way around.
Nevertheless there are perceptions of fossil fuel fired power plants being terribly polluting and of being the dominant source of man-made emissions while hydro-power plants are perceived as being totally non-polluting. These perceptions are mainly based on pre-determined political positions and not necessarily on measurements or reality.
A new study from Brazil looking at the impact of hydro power plants and the Balbina dam has been published in the Journal of Geophysical Research. One caveat of course with many such studies is that it is not based on measurements but on some measurement followed by hypotheses built into computer models. Nothing wrong with that of course but the weakness with many model results – as with climate models – is that the results can neither be verified or dis-proved by measurements.
Kemenes, A., B. R. Forsberg, and J. M. Melack (2011), CO2 emissions from a tropical hydroelectric reservoir (Balbina, Brazil), J. Geophys. Res., 116, G03004, doi:10.1029/2010JG001465
Electricity from hydropower can lead to several times the emissions of greenhouse gas emissions than produced from fossil fuels. At least from hydro-electric dams in the rain forest areas, according to a new study from Brazil.
The Balbina dam, which was built fifteen years ago, is located north of Amazonas state capital Manaus. When the rain forest area here was flooded large amounts of organic material ended up at the bottom of the pond. Rotting vegetation then caused large emissions of carbon dioxide and methane. According to this study this corresponded to three tonnes of carbon dioxide per megawatt-hour of energy produced, which is almost ten times that of a coal-fired power plants, and just over half of the emissions from burning fossil fuels in the city of São Paulo.
A recently published study of 85 hydroelectric dams in the world shows that emissions vary between different ponds, depending on size, age and what kind of soil is soaked. How big emissions Swedish hydroelectric dams produce has not yet been studied, but estimates indicate that they are significantly lower than from those in tropical areas in Brazil says Professor Philip Fernside of Instituto Nacional de Pesquisas da Amazônia (INPA) in Manaus. “It is true that dams in tropical areas such as the Amazon produces more than ponds in temperate climate, but there are emissions in these areas also” says Philip Fernside.
A pdf version of the paper is here.
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